1. Field of the Invention
The present invention relates to an internal-surface-scanning image recording apparatus for recording an image on a photosensitive medium held against the inner circumferential surface of a drum in the form of a partly cylindrical body, by scanning the photosensitive medium with a light beam that has been modulated by image information.
2. Description of the Related Art
Apparatus for recording an image on a photosensitive medium with a laser beam include a planar-surface-scanning image recording apparatus for applying a laser beam in a main scanning direction to a planar photosensitive medium which is being fed in an auxiliary scanning direction to record an image on the planar photosensitive medium, an external-surface-scanning image recording apparatus for applying a laser beam to a photosensitive medium mounted on the outer circumferential surface of a drum which is being rotated to record an image on the photosensitive medium, and an internal-surface-scanning image recording apparatus for applying a laser beam to a photosensitive medium mounted on the inner circumferential surface of a drum which is being rotated to record an image on the photosensitive medium. The internal-surface-scanning image recording apparatus is in widespread usage because the photosensitive medium mounted on the inner circumferential surface of the drum is prevented from being peeled off during a recording process, the recorded image has high dimensional accuracy, and the apparatus is capable of high-speed scanning and is highly economical.
FIG. 1 of the accompanying drawings schematically shows a conventional internal-surface-scanning image recording apparatus 2. As shown in FIG. 1, the internal-surface-scanning image recording apparatus 2 has a semicylindrical drum 4 with a photosensitive medium S mounted on its inner circumferential surface, a laser oscillator 6 for emitting a laser beam L, and a spinner 8 for scanning the photosensitive medium S with the laser beam L in main and auxiliary scanning directions.
The laser beam L emitted from the laser oscillator 6 is modulated by a modulating means 10 which comprises an acousto-optical modulator or the like for modulating the laser beam L with image information. Then, the modulated laser beam L passes through lenses 12, 14, is reflected by two reflecting mirrors 16, 18, and is applied to the spinner 8 by a condensing lens 20. The spinner 8 has a reflecting mirror 22 which is rotated about the central axis of the semicylindrical drum 4 to reflect the laser beam L and scans the photosensitive medium S with the laser beam L in the main scanning direction. At the same time, the spinner 8 moves in the auxiliary scanning direction along the central axis of the semicylindrical drum 4. In this manner, the image represented by the image information which has modulated the laser beam L is two-dimensionally recorded on the photosensitive medium S.
In the conventional internal-surface-scanning image recording apparatus 2, because the image is recorded on the photosensitive medium S only when the reflecting mirror 22 of the spinner 8 faces the photosensitive medium S, the laser beam L which is reflected by the reflecting mirror 22 when the reflecting mirror 22 of the spinner 8 does not face the photosensitive medium S is wasted. The conventional internal-surface-scanning image recording apparatus 2 cannot record the image at a high speed because the photosensitive medium S is scanned only in one cycle while the spinner 8 makes one revolution.
The above drawbacks may be overcome by using a cylindrical drum instead of the semicylindrical drum 4 to utilize the laser beam L effectively for increased exposure efficiency. However, it is difficult to attach the photosensitive medium S to and remove the photosensitive medium S from the cylindrical drum. Particularly, if an image is to be recorded on a printing plate, then the photosensitive medium S which is highly rigid needs to be curved to a large curvature, and may possibly be damaged when it is curved. Therefore, it is a time-consuming process to attach the photosensitive medium S to and remove the photosensitive medium S from the cylindrical drum, with the result that high-speed image recording cycles cannot be achieved.
High-speed image recording may be performed by increasing the speed at which the spinner 8 rotates. The spinner 8 is of an asymmetrical shape because the reflecting mirror 22 thereof is inclined at about 45xc2x0 to the axis about which the spinner 8 rotates. As a consequence, when the spinner 8 rotates, it tends to suffer rotational speed irregularities, and the reflecting mirror 22 may be deformed under centrifugal forces. When the spinner 8 rotates at a high speed, it is liable to produce noise and heat. These problems can be solved by reducing the size of the reflecting mirror 22. The reflecting mirror 22 of the reduced size, however, has a reduced area for receiving the laser beam L, and thus is unable to apply a sufficient amount of light energy to the photosensitive medium S. As a result, the resolution of the image is lowered, and also the quality of the image is lowered.
It is a general object of the present invention to provide an internal-surface-scanning image recording apparatus which is capable of recording an image at a high speed with a high level of accuracy on a photosensitive medium.
A major object of the present invention is to provide an internal-surface-scanning image recording apparatus which allows a photosensitive medium to be attached to and from a drum easily and efficiently for high-speed image recording on the photosensitive medium.
Another object of the present invention is to provide an internal-surface-scanning image recording apparatus which is capable of effectively utilizing a light beam to record an image on a photosensitive medium.
Still another object of the present invention is to provide an internal-surface-scanning image recording apparatus which can record an image on a photosensitive medium at a high speed without having to rotate a spinner at a high speed.
The above and other objects, features, and advantages of the present invention will become more apparent from the following description when taken in conjunction with the accompanying drawings in which preferred embodiments of the present invention are shown by way of illustrative example.